1. Field of the Invention
The present invention relates generally to glass forming and more particularly to preventing seizure and sticking of molten glass to metal forming molds as, for instance, glassware forming molds, and lubrication of such forming molds under extreme temperatures.
2. Description of the Prior Art
It is well known to form glass by shaping highly viscous molten glass in metal forms or molds until the glass cools sufficiently to maintain the induced form. One particularly demanding process for forming glass is the formation of glassware such as bottles. In this process, a glob of molten glass is typically first formed by a blank mold into a parison having a finished portion corresponding to the neck portion of the desired glassware. A neck ring engaging the finish portion of the parison is utilized to transport and place the parison in a blow mold, which is distinct from the blank mold, wherein blowing and cooling air or wind is conducted to the interior of the parison to force it into conformity with the blow mold and thereby to form the glassware.
Since molten glass will adhere to hot metal, and since the various mold sections will quickly wear if not lubricated, it is necessary to apply a release and lubricating agent to the molds. However, the glassware-forming process is exceedingly demanding upon release agents and lubricating compositions in that much of the heat from the molten glass is carried off through the metal molds in order to lower the surface temperature and viscosity of the formed glassware in that which permits the glassware to be self-supporting. Thus, since the molten glass is initially at a temperature of about 1800.degree. F., to about 2200.degree. F., and since the metal mold is usually hot below about 950.degree. F., to 975.degree. F., it will be appreciated that the parting agent interposed between the molten glass and the metal molds will be subjected to most extreme and intensified heat stresses. However, the molten glass will stick to metal if the release agent is vaporized and the mold parts will wear rapidly if the lubricating agent is not maintained.
Heretofore, a "dope", typically a dispersion of graphite in a light petroleum product such as kerosene, has been applied periodically by hand-held swab sticks to prevent sticking of glass to metal molds and to provide lubrication of the interacting mold sections. The drawbacks of this composition and application approach include the short period for which such dope is effective, the flashing of objectionable hydrocarbon vapors and the loss of glassware. Since the glass molds are at an elevated temperature, the petroleum product is flashed off quickly from the mold and constitutes an environment and fire hazard. Attempts to collect the vapor with hoods and other apparatus design have often resulted in unfavorable conditions. Often fires from the condensation of oils in the vicinity of the glass-forming machine results. Frequent venting of the petroleum products to the atmosphere is, of course, not desirable.
Production of glassware is also adversely effected by the use of the petroleum oils-graphite swabbing composition. When the petroleum product flashes off, it lowers the temperature of the mold thereby increasing the possibility of "check" defects in the glassware formed immediately after swabbing. Further, the first several articles formed after swabbing commonly have graphite particles embedded therein and must be rejected by inspectors as defective glassware. This results in a loss of pack or efficiency on the order of three percent or more of the glassware. This, of course, is an unfavorable condition.
Use of water-based carriers in place of the petroleum carriers for graphite, and other materials, have not heretofore been satisfactory. Objectionable odor problems and smoke, or fumes have marked the use of certain other proposed mold lubricants.
Further discussion of the long-existing problems with swabbing of molds and the effects to avoid or live with these problems found in U.S. Pat. Nos. 3,141,752; 3,480,422; 3,508,893; 3,523,016 and 3,623,856.
As might be expected, the above enumerated drawbacks and inefficiencies attendant to the dispersion of graphite in a petroleum base has led to numerous efforts to replace this composition with a more advantageous swabbing or parting agent. Except for narrow or marginal success under the less extreme of normal operating conditions, no suitable compounds have heretofore been known.
Elevated mold temperatures during glassware production make it difficult to successfully wet the mold surface when applying a swabbing composition. This is particularly true of formulations containing water. This problem is severely compounded when a constituent which will coat the mold, quickly cure and secure the graphite is included in the swabbing composition.
Examples of otherwise excellent lubricants and parting agents which have been tested in the demanding environment of glassware production and found to be inadequate include water-soluble graphite paste, high-pressure impingement with molybdenum disulfide with binder and various aqueous and or alcohol base swabs. Some minor previous success has been obtained with coating for 6 to 8 hour runs on conventional glass-forming machines, but these have proven to be extremely difficult to apply and have not provided reproducible results. Except for attempts to substitute another carrier for the petroleum product, few previous attempts have coped with the problem of swabbing during production.
While at first encounter, it would appear that the existence of and knowledge of many different lubricants would determine a satisfactory release and lubricating system for glass molds could easily be formulated, this has not been the case. However, as discussed in U.S. Pat. No. 3,495,962, the extreme conditions and varying, somewhat incompatible, requirements of glassware forming molds have presented formidable barriers to the technology. At the present, the above-discussed petroleum and graphite swabbing dopes is almost universally employed.
U.S. Pat. No. 2,052,629 further discusses glass and mold lubricants and release agents.